1. Field of the Invention
The present invention relates to an apparatus and a method for performing an attenuation function in a cable broadcast receiver. More particularly, the present invention relates to an apparatus and a method for performing an attenuation function of a signal using an attenuator in a cable broadcast receiver having a Low Noise Amplifier (LNA) that does not perform an attenuation function of a signal.
2. Description of the Related Art
As a broadcast service using a cable network evolves, an existing analog broadcast service evolves into a digital broadcast service. Accordingly, a broadcast receiver used by a subscriber evolves from an analog broadcast receiver to a digital broadcast receiver or a combined analog and digital broadcast receiver.
A typical broadcast system includes a broadcasting station for transmitting a broadcast signal, and a plurality of subscribers connected to the broadcasting station via an arbitrary medium. Each subscriber has a broadcast receiver for receiving a broadcast signal transmitted from the broadcasting station. The broadcast receiver includes a Low Noise Amplifier (LNA) and a tuner. The LNA attenuates a broadcast signal transmitted from the broadcasting station when the intensity of the signal is greater than a desired signal intensity, and amplifies the signal when the intensity of the signal is smaller than the desired signal intensity. The tuner tunes a frequency selected by a subscriber from broadcast signals transmitted from the broadcasting station. Therefore, a broadcast signal transmitted from the broadcasting station is transmitted to a subscriber via an arbitrary medium, and the transmitted broadcast signal is transmitted to the subscriber via the broadcast receiver.
Generally, the LNA is classified into an active LNA capable of performing both an amplification function and an attenuation function of a signal, and a passive LNA capable of performing only an amplification function of a signal. The active LNA can control an amount of amplification/attenuation, and is two to three times more expensive than a passive LNA since it includes an attenuation function. While the passive LNA has an advantage with respect to price, the passive LNA cannot attenuate an input signal by a desired amount, even when the intensity of the input signal is excessively high. That is, since the passive LNA can only fixedly amplify a preset value, the passive LNA cannot properly operate when the intensity of an input signal is excessively high.
More particularly, in a cable network, an analog channel has a high signal level compared to a digital channel. When extracting an analog channel in this cable network, a broadcast receiver that uses a passive LNA, which does not perform an attenuation function of a signal, obtains a very low Signal-to-Noise Ratio (SNR). This may cause a problem such as an abnormal screen or a frozen screen. Therefore, in this case, the broadcast receiver can only use a high-priced active LNA.